A field effect transistor, FET, is generally comprised of a channel that is doped to supply carriers, source and drain electrodes resistively coupled to opposite ends of the channel and a gate electrode that is spaced from the source and drain electrodes and electrically coupled to the channel by a Schottky barrier that effectively forms a diode in which the gate electrode is the anode. As well known, the flow of carriers between the source and drain electrodes is controlled by varying the bias of the gate electrode with respect to the source electrode so as to vary the cross sectional area in the channel through which carriers can pass. Fewer carriers flow when the cross sectional area is reduced than when it is enlarged. An advantage of a FET is that it responds quickly to the variation in the gate electrode bias so as to be useful in high speed switches and in the generation and amplification of high frequency electrical waves.
By adding a collector electrode to a FET between its gate and source electrodes as described in our U.S. Pat. No. 5,323,030 that is incorporated herein by reference, a heterostructure device is provided that is particularly useful in dense logic circuits because it can perform a number of functions e.g. depending on the gate bias it can produce oppositely phased amplified waves as well as complementary outputs at its collector and drain electrodes.
In the field effect real space transistor therein described, source and drain electrodes on top of a barrier layer are resistively coupled to opposite ends of a channel that is supplied with n carriers by bulk doping, and spaced gate and collector electrodes are mounted on the barrier between the source and drain electrodes. The gate electrode is electrically coupled to the barrier by a Schottky junction, and the collector electrode is resistively coupled to the barrier so as to form a mesa structure.
The device of the patent has characteristics wherein there is a desired region of operation in which the drain current, Id, is decreasing and the collector current, Ic, is increasing so as to provide the complementary outputs at the collector and drain previously referred to. The collector current is due to electrons that are transferred from the channel that would ordinarily go to the drain. Unfortunately, however, the desired region of operation only extended in one device to a gate voltage of 0.6 volts at which the device was destroyed by leakage current between the gate and collector. The gate does not supply electrons but some of the electrons that are drawn from the source to the near side of the gate become diffused in the barrier layer and are drawn to the more positive collector. The operating range is also reduced because of leakage of electrons between the gate and collector when the latter is relatively positive.